Validation of scramjet exhaust simulation technique at Mach 6

Current design philosophy for hydrogen-fueled, scramjet-powered hypersonic aircraft results in configurations with strong couplings between the engine plume and vehicle aerodynamics. The experimental verification of the scramjet exhaust simulation is described. The scramjet exhaust was reproduced for the Mach 6 flight condition by the detonation tube simulator. The exhaust flow pressure profiles, and to a large extent the heat transfer rate profiles, were then duplicated by cool gas mixtures of Argon and Freon 13B1 or Freon 12. The results of these experiments indicate that a cool gas simulation of the hot scramjet exhaust is a viable simulation technique except for phenomena which are dependent on the wall temperature relative to flow temperature

Validation of scramjet exhaust simulation technique

Scramjet/airframe integration design philosophy for hypersonic aircraft results in configurations having lower aft surfaces that serve as exhaust nozzles. There is a strong coupling between the exhaust plume and the aerodynamics of the vehicle, making accurate simulation of the engine exhaust mandatory. The experimental verification of the simulation procedure is described. The detonation tube simulator was used to produce an exact simulation of the scramjet exhaust for a Mach 8 flight condition. The pressure distributions produced by the exact exhaust flow were then duplicated by a cool mixture Argon and Freon 13B1. Such a substitute gas mixture validated by the detonation tube technique could be used in conventional wind tunnel tests. The results presented show the substitute gas simulation technique to be valid for shockless expansions

Modelling the many-body dynamics of heavy ion collisions: Present status and future perspective

Basic problems of the semiclassical microscopic modelling of strongly interactingsystems are discussed within the framework of Quantum Molecular Dynamics (QMD). This model allows to study the influence of several types of nucleonic interactions on a large variety of observables and phenomena occurring in heavy ion collisions at relativistic energies.It is shown that the same predictions can be obtained with several -- numerically completely different and independently written -- programs as far as the same model parameters are employed and the same basic approximations are made. Many observables are robust against variations of the details of the model assumptions used. Some of the physical results, however, depend also on rather technical parameters like the preparation of the initial configuration in phase space. This crucial problem is connected with the description of the ground state of single nuclei,which differs among the various approaches. An outlook to an improved molecular dynamics scheme for heavy ion collisions is given.Comment: 39 pages, 12 figure

Space as a low-temperature regime of graphs

I define a statistical model of graphs in which 2-dimensional spaces arise at low temperature. The configurations are given by graphs with a fixed number of edges and the Hamiltonian is a simple, local function of the graphs. Simulations show that there is a transition between a low-temperature regime in which the graphs form triangulations of 2-dimensional surfaces and a high-temperature regime, where the surfaces disappear. I use data for the specific heat and other observables to discuss whether this is a phase transition. The surface states are analyzed with regard to topology and defects.Comment: 22 pages, 12 figures; v3: published version; J.Stat.Phys. 201

Structural and mechanical properties of graded composite Al2O3/Ni obtained from slurry of different solid content

AbstractIn this work, an alumina-nickel graded hollow cylinders were prepared by the centrifugal slip casting. In the paper, the results for samples formed from slurries with different solid content: 45 vol.%, 40 vol.% and 35 vol.% are presented. The structure of the samples after sintering was examined by X-ray diffraction (XRD). The microstructure of the composite, especially the nickel particle size distributions were investigated by using scanning electron microscopy (SEM). An image analyzer has been used for the measurement of volume fraction of the nickel particles in the composites. The hardness was measured by using a Vickers hardness-testing. Based on hardness measurements KIC value were determined. The XRD results confirmed only two phases: Ni and α-Al2O3 in all samples. The preliminary macroscopic observation as well as SEM showed, that the microstructure of the sample cross-section is not homogeneous. Microstructural characterization revealed the gradation of nickel content along the radial direction of hollow cylinder. Three zones were distinguished, from outer surface towards the inner side of the tube. The maximum of volume fraction of nickel particles was obtained at the middle zone of the composites. The results of hardness-testing revealed that the maximum hardness values were observed in region at the inner edge of the casting due to an absence of nickel particles

Oxygen Deficiency Hazard (ODH) Monitoring System in the LHC Tunnel

The Large Hadron Collider (LHC) presently under construction at CERN, will contain about 100 tons of helium mostly located in equipment in the underground tunnel and in caverns. Potential failure modes of the accelerator, which may be followed by helium discharge to the tunnel, have been identified and the corresponding helium flows calculated [1, 2, 3]. In case of helium discharge in the tunnel causing oxygen deficiency, personnel working in the tunnel shall be warned and evacuate safely. This paper describes oxygen deficiency monitoring system based on the parameter of limited visibility due to the LHC tunnel curvature and acceptable delay time between the failure and the system activation

Charging and coagulation of dust in protoplanetary plasma environments

Combining a particle-particle, particle-cluster and cluster-cluster agglomeration model with an aggregate charging model, the coagulation and charging of dust particles in various plasma environments relevant for proto-planetary disks have been investigated. The results show that charged aggregates tend to grow by adding small particles and clusters to larger particles and clusters, leading to greater sizes and masses as compared to neutral aggregates, for the same number of monomers in the aggregate. In addition, aggregates coagulating in a Lorentzian plasma (containing a larger fraction of high-energy plasma particles) are more massive and larger than aggregates coagulating in a Maxwellian plasma, for the same plasma densities and characteristic temperature. Comparisons of the grain structure, utilizing the compactness factor, {\phi}{\sigma}, demonstrate that a Lorentzian plasma environment results in fluffier aggregates, with small {\phi}{\sigma}, which exhibit a narrow compactness factor distribution. Neutral aggregates are more compact, with larger {\phi}{\sigma}, and exhibit a larger variation in fluffiness. Measurement of the compactness factor of large populations of aggregates is shown to provide information on the disk parameters that were present during aggregation

Microscopic Analysis of Thermodynamic Parameters from 160 MeV/n - 160 GeV/n

Microscopic calculations of central collisions between heavy nuclei are used to study fragment production and the creation of collective flow. It is shown that the final phase space distributions are compatible with the expectations from a thermally equilibrated source, which in addition exhibits a collective transverse expansion. However, the microscopic analyses of the transient states in the reaction stages of highest density and during the expansion show that the system does not reach global equilibrium. Even if a considerable amount of equilibration is assumed, the connection of the measurable final state to the macroscopic parameters, e.g. the temperature, of the transient ''equilibrium'' state remains ambiguous.Comment: 13 pages, Latex, 8 postscript figures, Proceedings of the Winter Meeting in Nuclear Physics (1997), Bormio (Italy

Microscopic calculations of stopping and flow from 160AMeV to 160AGeV

The behavior of hadronic matter at high baryon densities is studied within Ultrarelativistic Quantum Molecular Dynamics (URQMD). Baryonic stopping is observed for Au+Au collisions from SIS up to SPS energies. The excitation function of flow shows strong sensitivities to the underlying equation of state (EOS), allowing for systematic studies of the EOS. Effects of a density dependent pole of the $\rho$-meson propagator on dilepton spectra are studied for different systems and centralities at CERN energies.Comment: Proceedings of the Quark Matter '96 Conference, Heidelberg, German